Many machines include power systems configured to provide power to perform various tasks, such as propelling the machine. Many power systems include a prime mover configured to produce power by rotating a rotary output member and a transmission having a rotary input member drivingly connected to the rotary output member of the prime mover. Some power systems also include a motor/generator drivingly connected to the rotary output member of the prime mover and/or the rotary input member of the transmission.
Some power systems include a fluid coupler, such as a torque converter, connected between the rotary output member of the prime mover and the rotary input member of the transmission. Such fluid couplers are capable of transmitting power between the rotary output member of the prime mover and the rotary input member of the transmission, while allowing the speeds of the rotary output member of the prime mover and the rotary input member of the transmission to vary substantially independently. Thus, a fluid coupler connected between the rotary output member of a prime mover and the rotary input member of a transmission ensures smooth power transfer between the prime mover and the transmission during steady state operation and also during sudden changes in the operating state of the prime mover and/or the transmission. However, there may be circumstances in which it is desirable to drivingly connect the rotary output member of the prime mover to the rotary input member of the transmission at a fixed speed ratio.
U.S. Pat. No. 6,913,558 to Mori et al. (“the '558 patent”) shows a power transmission system having an engine and a motor generator connected to a transmission by a torque converter that has a lockup clutch. In the power transmission system of the '558 patent, the engine and the motor generator are directly connected to one another. The engine and motor generator are connected to one side of the torque converter, and a rotary input member of the transmission is connected to the other side of the torque converter. The torque converter transmits torque via fluid when the lockup clutch is disengaged, and the torque converter drivingly connects the rotary input member of the transmission to the engine and motor generator at a fixed drive ratio when the lockup clutch is engaged. The operating state of the lockup clutch is controlled by a hydraulic control circuit. A “power drive unit” controls the motor generator.
Although the power transmission system of the '558 patent includes a torque converter with a lockup clutch for selectively engaging the rotary input member of the transmission to the engine and motor generator at a fixed speed ratio, certain disadvantages persist. For example, the '558 patent does not disclose any means of coordinating the operation of the motor generator and the lockup clutch. As a result, the power transmission system of the '558 patent may fail to capitalize on opportunities to utilize the motor generator more effectively by controlling the lockup clutch in a manner that complements the operating state of the motor generator. Additionally, because the power transmission system of the '558 patent has the engine and the motor generator connected to the same side of the torque converter, the prime mover and the motor/generator must always operate at the same speed. Thus, the power transmission system of the '558 patent may be unable to capitalize on circumstances in which it may be beneficial to operate the motor generator at a different speed than the engine.
The power system and control methods of the present disclosure solve one or more of the problems set forth above.